One of the most popular ETFs recently is a fund that invests in U.S. inflation-protected bonds.

Investors added $638 million to iShares Barclays TIPS Bond Fund (NYSEArca: TIP) in May, according to data from the ETF Industry Association. The $23.5 billion fund was among the top sellers last month.

The inflows suggest some investors are exploring fixed-income funds for inflation protection outside gold and commodities ETFs.

After Friday’s weak jobs report, speculation is growing that the Federal Reserve will announce further stimulus. Meanwhile, there is lingering talk the ECB will be forced to step in again with more easing measures to help Europe’s banking sector and debt crisis.

With Treasury Inflation-Protected Securities or TIPS, the bonds’ principal is linked to changes in the Consumer Price Index.

However, it’s important to remember that since the ETFs invest in Treasury bonds, they can be hurt by rising interest rates.

“TIPS will not perform well if real yields rise along with rising interest rates,” said Russ Koesterich, iShares chief investment strategist.

Other ETFs for this asset class include PIMCO 1-5 Year TIPS (NYSEArca: STPZ), SPDR Barclays Capital TIPS (NYSEArca: IPE) and Schwab U.S. TIPS (NYSEArca: SCHP).